Synthetically produced silicas play an important role as an ingredient in many of today's toothpaste formulations. Such silicas are relatively safe, nontoxic, ingredients which are compatible with other toothpaste ingredients, including glycerin, sorbitol (or xylitol), thickening agents, detergents, coloring and fragrance materials and optionally fluoride and other actives. Further, silicas act as an abrasive to clean teeth, remove plaque and food debris.
As an abrasive or polishing agent, silicas debride and physically scrub the external surface of the teeth. This scrubbing action removes the organic film (i.e. the pellicle), formed of salivary proteins which covers the teeth and which is known to become stained and discolored by foods, such as coffee, tea and berries, as well as, by tobacco smoke, cationic antibacterials, and chromogenic bacteria. Such physical removal of the stained pellicle is a simple and effective means of removing the undesirable surface staining and discoloration which occurs daily. Further, such physical removal of the pellicle also removes plaque bacteria on the pellicle surface.
Synthetic silicas include both silica gels and precipitated silicas which are prepared by the neutralization of aqueous silicate solutions with a strong mineral acid. In the preparation of silica gel, a silica hydrogel is formed which is then typically washed to low salt content. The washed hydrogel may be milled to the desired size, or otherwise dried, ultimately to the point where its structure no longer changes as a result of shrinkage. When preparing such synthetic silicas, the objective is to obtain abrasives which provide maximal cleaning (i.e. removal of stained pellicle) with minimal damage to the tooth enamel and other oral tissue. Dental researchers are continually concerned with identifying synthetic silicas meeting these objectives.
U.S. Pat. No. 4,153,680 and GB Patent Application 2,038,303A both disclose the general use of silica hydrogels or hydrated silica gels as dentifrice polishing agents. U.S. Pat. No. 4,632,826 discloses the use of hydrated silica gels in combination with a weakly calcined alumina polish, to form a combination abrasive system. U.S. Pat. Nos. 4,943,429, 5,176,899 and 5,270,033 provide lists of alternative polishing agents, such lists including hydrated silica gels.
In spite of the disclosures relating to silica hydrogels and other compositions for oral cleaning, there is still a need for additional compositions providing improved pellicle cleaning, improved removal of plaque and food debris, all with minimal abrasion of the tooth enamel and other oral tissue.